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C. Jamieson (Cal Poly State University, San Luis Obispo), J. B. Dalton (NASA Ames Research Center)
Infrared reflectance spectroscopy is a powerful tool for determining the composition of solar system objects. The visible to near-infrared (VNIR) spectral range is widely used in the outer solar system because this wavelength range is centered at the highest point of the solar output spectrum. Spacecraft instruments relying upon this technique include the Galileo Near-Infrared Mapping Spectrometer (NIMS), which observed the Jovian system, the Cassini Visible and Infrared Mapping Spectrometer (VIMS), which is nearing a rendezvous with Saturn and its satellite, Titan, and instruments under consideration for the Pluto/Kuiper Belt mission.
In order to properly analyze the VNIR observations of icy satellites, detailed laboratory studies of the surface components must be available for comparison. To be useful, reference spectra must be measured 1) in reflectance, 2) in a wavelength range appropriate to the observations (0.35-5.1 microns for the Cassini VIMS), and 3) at a temperature that is relevant to the celestial body of interest. Most laboratory spectra are recorded in absorbance or transmittance, which are not convertible to a reflectance spectrum due to scattering effects. Also, many materials, such as water, show significant spectral variation with changes in temperature. A search through the published literature for spectra relevant to icy worlds reveals a number of candidate materials that have yet to be measured according to these three basic criteria.
A graphical representation of the present spectroscopic knowledge space as represented in the literature has been compiled for icy satellites. While some molecules, like water and methane, are well studied, other common molecules such as methanol and formaldehyde are not well characterized by reflectance spectroscopy. This organized database of completed work allows for the easy identifications of regions that need further laboratory effort.
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.